Parathyroid hormone-related protein expression in the human colon: immunohistochemical evaluation

Parathyroid hormone-related protein (PTHrP) has been shown to be the primary factor responsible for humoral hypercalcemia of malignancy. In addition to its hypercalcemic action, PTHrP has been implicated as an autocrine modulator of growth and differentiation, as well as an early response gene in some tissues. Several different types of tumors have been evaluated for the presence of PTHrP immunoreactivity. In the present study, we evaluated the expression of PTHrP by immunohistochemical staining in tissue samples from normal colorectal mucosa, polyps, and colorectal carcinoma removed from the same patients (n = 10 each). We have used a commercially available monoclonal antibody directed against epitopes between amino acids [53-64] which share no homology to parathyroid hormone (PTH). In normal colon, 94.3 per cent of the tissue samples were negative for PTHrP immunoreactivity. In polyps of the colon, only 22.6 per cent of the cells showed positive immunostaining, whereas 91.5 per cent of the samples from colon cancer stained positive for PTHrP. In the case of polyps, the intensity of staining was 1-3+; however, all of the samples from adenocarcinoma stained with 4+ intensity. In the positive samples, the immunoreactivity was present throughout the cytoplasm of the glandular epithelium. Omission of primary antibody, as well as substitution of the primary antibody by a negative control monoclonal antibody or non-immune rabbit serum, resulted in a negative reaction. All analyses were performed in duplicate, and the data have been presented as mean +/- SEM. Differences in normal polyps, carcinoma of the colon, and PTHrP expression were tested for statistical significance by student's t test. Our results show the expression of PTHrP is enhanced in colon cancer tissue as compared to normal colorectal mucosa and polyps. In addition, the expression appears to be greater in polyp than in normal colon. The role of PTHrP in the pathogenesis of colon cancer deserves further study.